The invention relates to a plug-in insert for electrical communications apparatus. In such apparatus, for mechanical allocation between an insert and an insert receiving unit, guide rails are provided, and for electrical contacting at the end of the insertion phase, electrical plug-in elements are provided. For unmistakable allocation of the two units relative to one another, identification pins are provided in the one unit, and matching openings are provided in the other unit which interengage prior to commencement of the electric contacting and prevent the contacting of a false unit.
A device of this type is described in greater detail in German Offenlegungsschrift 33 23 821, incorporated herein by reference. The coding pins which are capable of springy insertion on the insert on the one hand, and which are capable of springy insertion on the insert receiving unit on the other hand, are all designed to be equally long and, in the case of faulty coding, strike one another at a sufficient distance before the engagement of the electrical plug-in elements.